1-800-691-1991 | 9am - 8pm ET

Advanced transport modes (HotAdd and SAN) fail over to NBD mode


Advanced transport modes (Virtual Appliance (HotAdd) or Direct Storage access) may not work, failing over to the NBD transport mode instead.

If you are seeing error "Cannot use advanced transport modes, failing over to NBD" you should check the HotAdd attacher agent log (default location - C:\ProgramData\Veeam\Backup\Job_name\Agent.Job_name.VM_name.Hotadd.Attacher.log) on affected backup proxy/proxies, you may encounter following “SSL exception” error:
[08.04.2020 8:26:46.680] <   724> vdl| [vddk] 2020-04-08T20:26:46.680-07:00 error -[00724] [Originator@6876 sub=Default] SSL Async Handshake Timeout : Read timeout after approximately 25000ms. Closing stream <SSL(<io_obj p:0x000001ef0b15eb68, h:1100, <TCP 'x.x.x.x : 49746'>, <TCP 'x.x.x.x : 443'>>)>
[08.04.2020 8:26:51.668] <  5412> vdl| [vddk] 2020-04-08T20:26:51.668-07:00 error -[05412] [Originator@6876 sub=IO] HandshakeCb; <SSL(<io_obj p:0x000001ef0b15eb68, h:-1, <TCP 'x.x.x.x : 49746'>, <TCP 'x.x.x.x : 443'> FD Closed>)>; error: class Vmacore::Ssl::SSLHandshakeTimeoutException(SSL Exception: The file handle supplied is not valid)


The SSL certificate and thumbprint verification is a mandatory process starting from VMware VDDK 6.0. Advanced transport modes (Virtual Appliance (HotAdd) or Direct Storage access) are utilizing TLS protocol unlike the NBD mode.


If your vCenter has a self-signed certificate tree, install all certificates on all proxies.


Veeam Backup & Replication, Veeam Cloud Connect
9.5 and higher
Last Modified:
Please rate how helpful this article was to you:
5 out of 5 based on 1 ratings
Thank you for helping us improve!
An error occurred during voting. Please try again later.

Couldn't find what you were looking for?

Below you can submit an idea for a new knowledge base article.
Report a typo on this page:

Please select a spelling error or a typo on this page with your mouse and press CTRL + Enter to report this mistake to us. Thank you!

Spelling error in text

Knowledge base content request
By submitting, you agree that your personal data will be managed by Veeam in accordance with the Privacy Policy.

ty icon

Thank you!

We have received your request and our team will reach out to you shortly.


error icon

Oops! Something went wrong.

Please go back try again later.